I personally think the iPod hardware "refresh" will occur on September 18, 2007.

I do think we'll see the following:
iPod shuffle--no hardware changes externally, but there will now be a 2 GB model in addition to a 1 GB model. 1 GB will now cost US$70 and 2 GB model will cost US$100.
iPod nano--no hardware changes externally, but 2 GB model dropped, 4 GB model in silver case becomes low end model, 8 GB model becomes "mainstream" model with up to ten different color cases, and new 16 GB model in black and red case only. Prices will be lowered (US$150 for 4 GB, US$200 for 8 GB, and US$250 for 16 GB).
iPod nano video--new model that looks like a 2G nano "writ large" with wider case (but same sized Click Wheel) that accommodates a display almost as large as the 5.5G iPod so it can play back videos. It will be available in 8 GB and 16 GB flash memory storage versions in five different color cases. Cost will be US$250 for 8 GB model and US$299 for 16 GB model.
6G iPod video--all new model in a case about the same size as 5.5G iPod that uses a fullscreen display with touchscreen interface. It will be available with 80 GB and 120 GB hard disk storage. Cost will be US$350 for 80 GB model and US$399 for 120 GB model.